Is High Quality Sensing Really Necessary for Opportunistic Spectrum Usage?

The major requirement for Cognitive Radio (CR) based opportunistic spectrum re-usage is reliable protection of the primary communication. This calls for a reliable detection of the presence of the Primary Users (PUs) as well as for an immediate reconfiguration of the secondary communication: Each time the PU has been detected, the Secondary Users (SUs) have to vacate the respective part of the spectrum and continue their communication elsewhere. Unfortunately enough, also false positives in the sensing process trigger the same type of reconfiguration, leading to more reconfigurations than actually necessary. Therefore, the efficiency of this reconfiguration process is of high interest. For a frequently postulated OFDM based spectrum pooling SU system two basic questions are considered: (1) How should the parameters of the secondary communication link be selected in order to achieve a stable Quality of Service (QoS) in spite of reconfigurations, and (2) how strongly is the QoS of the SU influenced by reconfigurations caused by a non ideal sensing process, i. e. by an excessive number of false positives.